Onto a recordable or rewritable optical disc such as a DVD-R (DVD-Recordable) or a DVD-RW (DVD-Re-recordable), information is recorded thereon by irradiating a laser light on a recording surface of the disc. Since a temperature rises at a part on the recording surface of the optical disc to which the laser light is irradiated, a change occurs to an optical recording medium forming the optical disc, and thereby a recording mark is formed onto the recording surface.
Therefore, by modulating the laser light by using a recording pulse having a time width corresponding to information to be recorded, thereby to generate a laser pulse having a length corresponding to a signal to be recorded is generated, and by irradiating the generated laser pulse onto the optical disc, the recording mark having a length corresponding to the information to be recorded can be formed onto the optical disc.
Meanwhile, there is recently used such a control technique of a laser power that one recording mark is formed not by one laser pulse but by a pulse train unit having plural short pulses (also called “pulse train”). In addition, there is proposed a technique of using a recording pulse waveform having a top pulse period, a last pulse period and an intermediate bias period therebetween, instead of a recording pulse waveform having the pulse train, at the time of high-speed recording (see Japanese Patent Applications Laid-open under No. 2003-77128 and No. 2003-85753, for example).
In the above-mentioned recording systems, the laser power in the pulse train period, the top pulse period and the last pulse period has a fixed value irrespective of a mark length. For example, in a write strategy for 8-times high speed recording of a DVD-R, 3T and 4T marks are recorded by a single recording pulse, and a mark equal to or larger than 5T is recorded by the recording pulse waveform having the top pulse period, the last pulse period and the intermediate bias period, as describe above. However, levels thereof, i.e., recording powers, are same.
On the other hand, in a system of 4-times high speed recording of a DVD+R, marks of all lengths are formed by a single recording pulse. However, the levels (i.e., the recording powers) of the 3T and 4T recording pulses become larger than the level of the mark equal to or larger than 5T. Concretely, a ratio of the recording powers of the 3T mark, the 4T mark and the mark equal to or larger than 5T is determined to be constant.
When the recording is performed by the recording pulse waveform having the recording power of one kind or the recording power of the fixed ratio, as recording speed is high, a modulation degree becomes large. But when the modulation degree becomes large, such probability that an adverse effect is given to an AR (Aperture Ratio), an LPP error, an ADIP error becomes large. In addition, asymmetry at which thermal interference occurs becomes close to a lower limit of a standard value or a range enabling reproduction, and a margin thereof becomes narrow.